During the laundering operation of fabrics it is highly desirable to provide the fabric, particularly man-made fabrics produced from synthetic fibres, with soil release properties.
Due to the hydrophobic nature of fabrics composed of partially or completely synthetic fibres, the removal of greasy soils and stains therefrom is particularly difficult. In order to address this problem, soil release polymers may be incorporated into the detergent composition. During laundering the soil release agents are adsorbed onto the surface of the fabric, thereby inducing greater hydrophobicity to the fabric surface. Once the fabric is treated with a soil release agent, the ease of removal of soils and stains from the surface of the fabric is considerably improved.
The main types of soil release agents incorporated into detergent compositions, which provide benefits to primarily hydrophobic synthetic fabrics include synthetic soil release agents, preferably terephthalate based and polysaccharide ethers. Polysaccharide ethers such as cellulose ethers have been described for example in GB 1 534 641, which discloses nonionic surfactant detergent compositions comprising cellulose ether soil release agents such as alkyl and hydroxyalkyl cellulose ethers.
The soil release performance of the polysaccharide ethers may be improved upon greasy/oily stains by increasing the degree of substitution and the chain length of the subsitutent. This results in the polysaccharide ether being only weakly and temporarily bound to the fabric surface and thus easily removed once soiling has occurred.
The soil release performance of the polysaccharide ethers may further improved by increasing the amount of polysaccharide ether used and or by increasing the molecular weight or degree of polymerisation (dp). However, high molecular weight polysaccharide ethers are known to have detrimental effects on the clay soil removal and anti-redeposition performance of the detergent composition in which they are incorporated. This is particularly evident on fabrics after a number of repeated washing cycles or when high dosage or concentrations of detergent composition are utilised to clean heavily soiled fabric. Furthermore, this problem is also acute on fabrics which contain a high percentage of synthetic fibres.
During the laundering operation it is also desirable reduce the effects of aging on the fabrics. Aging of naturally based fabrics results in the damage of the top surface fibres which increases the number of soil collection sites and results in the fabric gaining an unhomogeneous feel. This may be addressed by the incorporation of cellulolytic enzymes into detergent compositions. The cellulolytic enzyme removes the damaged surface fibres and thereby improves stain removal, fabric appearance and reduces the hardness of the fabric after multiple washing. However, the cellulolytic enzyme by its very nature hydrolyses and depolymerises polysaccharide ethers having 1,4 .beta.-glucosidic bonds. This problem of cellulase and polysaccharide ether incompatibility is particularly acute for low substituted polysaccharide ethers which appear more `cellulosic` in nature.
Thus, it is an aim of the present invention to provide a detergent composition comprising a cellulolytic enzyme and a nonionic polysaccharride ether, whereby the soil release performance of the polysaccharide is enhanced by the presence of the cellulolytic enzyme.
It has now been found that this objective can be achieved by the use of selected nonionic polysaccharide ethers having specified degrees of polymerisation and substitution. It is believed that the nonionic polysaccharide ethers of the present invention can be deposited onto the fabric surface prior to the start of degradation by the cellulolytic enzyme.
In addition, a further advantage of the present invention is that the subsequent cellulolytic enzyme attack upon the polysaccharides after their deposition on the fabric, aids the removal of trapped particulate soils and clay soil removal.
Another advantage of the present invention is that high molecular nonionic polysaccharide ethers may be used in combination with cellulase to provide soil release benefits without affecting the clay soil removal performance.
A further advantage of the present invention is that the detergent composition delivers improved whiteness performance and fabric feel.
Nonionic polysacchairdes and cellulolytic enzymes have been described in the art. EPO 495 257 discloses a compact detergent composition comprising high activity cellulolytic enzyme. Anti-redepositioin agents such as cellulose derivatives are disclosed, in particular methyl cellulose, carboxymethylcellulose (CMC) and hydroxyethyl cellulose. Only CMC and cellulolytic enzyme is exemplified and there is no disclosure of the specific combination of cellulolytic enzyme and cellulose ether.
EPO 320 296 discloses fabric softening additives for detergent compositions comprising a water soluble nonionic ethyl hydroxyethyl cellulose having an HLB of 3.3 to 3.8, a dp of 50 to 1200 and a ds of 1.9 to 2.9. Enzymes including cellulolytic enzyme are disclosed. The combination of cellulose ether and cellulolytic enzyme is not exemplified.
EPO 213 730 discloses detergent compositions with fabric softening properties comprising a nonionic substituted cellulose ether derivative, having a ds of from 1.9 to 2.9 and dp of 50 to 1200. Enzymes such as cellulolytic enzyme are mentioned. The combination of cellulose ether and cellulolytic enzyme is not exemplified.
EPO 173 397 discloses detergent compositions comprising a cationic softening agent and a fungal cellulolytic enzyme. Soil suspending agents such as water soluble salts of CMC, carboxyhydroxymethyl cellulose are disclosed. Their preferred dp or ds values are not mentioned.